1. Field of the Invention
The present invention relates to an antenna device provided with two antenna elements.
2. Description of Related Art
Conventionally, as a car antenna device to be set on a vehicle roof, an antenna apparatus provided with a plurality of antennas such as for AM/FM radio broadcasting, for satellite radio broadcasting, for GPS (Global Positioning System), for telephone, for television broadcasting and so forth is known. By using these antennas, such antenna device can receive radio waves of a plurality of frequency bands.
Further, an antenna device provided with a rod antenna and a patch antenna is known as the above mentioned car antenna device. For example, there is known a car antenna device provided with a rod antenna for receiving AM/FM radio broadcasting and a circuit substrate for the rod antenna and also provided with two antenna units respectively for GPS and satellite radio broadcasting (see the specification of U.S. Pat. No. 7,633,452). Each antenna unit includes a patch antenna, a circuit board and a shielding case covering the circuit board. On each circuit board, a circuit element such as LNA (Low Noise Amplifier) to amplify the signal received by each antenna is mounted. Each antenna unit is mounted on the circuit board of the rod antenna. The circuit board of the rod antenna is screwed to a die-cast base having a fixation section for fixing the antenna device on the vehicle roof.
The patch antenna is constituted of a patch electrode, a grounding electrode, a dielectric board between the patch electrode and the grounding electrode and an electrode pin being connected with the patch electrode and penetrating the dielectric board. The gain of the patch antenna is increased by expanding the area of the grounding. There is known an antenna device provided with a patch antenna and a shielding case in which the circuit board of the patch antenna is housed and the patch antenna is provided on the top board of the shielding case, wherein the top board is overhung around the grounding electrode and the patch electrode is connected to the circuit board via the shielding case, in order to have a large are for grounding (see JP 2004-72320).
However, in the conventional antenna device provided with a rod antenna and patch antennas, the antenna units of the patch antennas are mounted on the circuit board of the rod antenna and the circuit board of the rod antenna is screwed onto the die-cast base. Therefore, a space for mounting the antenna units of the patch antennas on the circuit board of the rod antenna is needed in addition to a space for screwing the circuit board of the rod antenna onto the die-cast base. Therefore, a large space is used for the antenna.
Especially, when a shielding case in which the top board is larger than the area for the grounding electrode is used as in the case of the conventional patch antenna device where a patch electrode is connected to the circuit board via the shielding case, it is preferred that the space used for mounting the antenna units of the patch antennas on the circuit board of the rod antenna is smaller in order to realize space-saving in the antenna apparatus.